Fix area/instrument i18n in EntityLink

Fixes a couple issues in the previous code:

 * It should've been checking for areas, not artists. Artists don't have
   translated names (not counting aliases), but areas which are
   countries do. You can see this is the behavior of the original TT
   macros, too: areas and instruments default to l_name for their
   content.

 * We don't serialize any l_name property. We have to get the translated
   name from the appropriate gettext domain.

root/static/scripts/common/components/EntityLink.js

@@ -10,6 +10,8 @@ const React = require('react');
 const Frag = require('../../../../components/Frag');
 const {ENTITIES, AREA_TYPE_COUNTRY} = require('../constants');
 const {l} = require('../i18n');
+const {l_countries} = require('../i18n/countries');
+const {l_instruments} = require('../i18n/instruments');
 const bracketed = require('../utility/bracketed');
 const entityHref = require('../utility/entityHref');
 const formatDatePeriod = require('../utility/formatDatePeriod');
@@ -103,8 +105,10 @@ const EntityLink = (props = {}) => {
     hover = entity.sort_name + bracketed(comment);
   }
 
-  if (entityType === 'artist' || entityType === 'instrument') {
-    content = content || entity.l_name;
+  if (entityType === 'area') {
+    content = content || l_countries(entity.name);
+  } else if (entityType === 'instrument') {
+    content = content || l_instruments(entity.name);
   }
 
   content = content || ko.unwrap(entity.name);

root/static/scripts/common/i18n/countries.js

@@ -0,0 +1,20 @@
+/*
+ * @flow
+ * Copyright (C) 2018 MetaBrainz Foundation
+ *
+ * This file is part of MusicBrainz, the open internet music database,
+ * and is licensed under the GPL version 2, or (at your option) any
+ * later version: http://www.gnu.org/licenses/gpl-2.0.txt
+ */
+
+import wrapGettext from './wrapGettext';
+
+const l_countries = wrapGettext('dgettext', 'countries');
+const ln_countries = wrapGettext('dngettext', 'countries');
+const lp_countries = wrapGettext('dpgettext', 'countries');
+
+export {
+  l_countries,
+  ln_countries,
+  lp_countries,
+};

root/static/scripts/common/i18n/instruments.js

@@ -0,0 +1,20 @@
+/*
+ * @flow
+ * Copyright (C) 2018 MetaBrainz Foundation
+ *
+ * This file is part of MusicBrainz, the open internet music database,
+ * and is licensed under the GPL version 2, or (at your option) any
+ * later version: http://www.gnu.org/licenses/gpl-2.0.txt
+ */
+
+import wrapGettext from './wrapGettext';
+
+const l_instruments = wrapGettext('dgettext', 'instruments');
+const ln_instruments = wrapGettext('dngettext', 'instruments');
+const lp_instruments = wrapGettext('dpgettext', 'instruments');
+
+export {
+  l_instruments,
+  ln_instruments,
+  lp_instruments,
+};